Thread forming method and apparatus



y 1953 H. E. PFINGSTON 2,645,954

THREAD FORMING METHOD AND APPARATUS Filed March 30, 1949 I 2 Sheets-Sheet 1 I /& T r I INVENTOR.

July 21, 1953 H, E. PFINGSTON THREAD FORMING METHOD AND APPARATUS 2 Sheets-Sheet 2 Filed Marbh 50, 1949 /7 JNVENTOR. Mi

arrafizvg Patented July 21, 1953 THREAD N Tf oFFicE AND Homer'E. Pfings'ton, Evansville, Ind., 'assignor to Serve], Inc., New York; N. Y., a'corporation of Delaware Application March 30, 1949, Serial No. 84,408

4 Claims.

This invention relates to a method of and a tool for forming threads on a surface of a work piece.

This invention relates more particularly to forming multiple fine deep threads on a work piece surface by a rolling action.

This application relates back for common subject matter to my copending application Serial No. 715,883, filed December 12, 1946, now abandoned. I r H Theoretically, or onpaper, it is possible to design a tool that will form any reasonable number of threads on a surface per unit length thereof. However, when it comes to actually making such av tool, it is found that if the threads are to have any appreciable depth the cutting or rolling edges of the tool are so delicate that the life of the tool is very short. Furthermore, if'very fine thread be desired, the rolling edges of the tool are so close together that it is practically impossible to form such edges by an ordinary grinding process.

I have overcome the above difllculties by providing a tool wherein a plurality of sturdy rolling edges are formed on a roller, which edges are spaced a sufficient distance apart that they may be readily formed by conventional grinding processes. The plurality of sturdy rolling edges are given a slight taper and are spaced in a manner that a relatively wide helical groove or thread is gradually formed on a work piece surface. The number of threads per unit length of work piece formed by the sturdy rolling edges is only a fraction of that desired on the finished product,

and the crest or ridge of the thread is relatively wide. However, by providing one or more sharp rolling edges on the roller spaced a proper distance from the rearmost of the plurality of sturdy rolling edges, the number of threads per unit length may be multiplied. t

The number of threads per unit of length may be doubled by providing a single sharp rolling edge and spacing such sharp edge from the rearmost of the other rolling edges in a manner that the sharp edge splits the ridge formed by the 4:

are formed on the work piece surface.

With my improved roller type tap continuous helical threads are rolled on the work piece without the removal of any materialtherefrom. The material from the helical grooves "is forced up drawings, wherein:

formed.

into helical ridges which greatly increases the depth of the grooves without materially decreasing the thickness of the work piece. The use of my, improved'roller type tap permits a greater number of threads per unit of length than was practical heretofore. The rollers are provided with multiple teeth orrolling edges thus increas ing production speed." The teeth on the rollers are given a slight taper so that the depth of the thread is increased gradually thereby reducing wear'on the rollers. Like an ordinary tap, once my improved tap is' started into a-work piece it pulls itself therethrough as it is rotated it does not need a lead screw. Although not limited to, my inventionfinds particular applicationinthe forming of very fine threadsor capillary grooves on a'heat transfer surface, such as theevaporator and/or absorber. tubes of a refrigerating apparatus, wherein it is desirable that a small quantity of liquid be spread as a thin film over a relatively large surface.

'The. invention together with its objects and advantages is setforth in more technical detail in the'following description and'accompanying Fig. 1 is a perspective view of a roller tap incorporating my invention;

Fig. 2 is' a top plan view of the tap shown in F Fig. 3 is a bottom plan view of the tap shown in Fig. 1;

Fig. 4 is a developed view of my improved tap, with certain parts omitted for clarity of illustra- Fig. 5 is a transverse sectional view taken substantially on line 5-1-5 of Fig. 7, but showing the tap within'fa tube that is being threaded; .Fig. 6is a transverse sectional view takenon line 66 of Fig. 7.; I

Fig. '1 isa longitudinal sectional view taken substantially on line 1-1 of Fig. 5, but with the tube'omitted; and 1 u Fig. 8 is an enlarged fragmentary longitudinal sectional view showing one of the tap rollers and its relation to a tube inwhich threads are being Basically, my improved tap includes body members .IO and II held together by a machine screw I2 and a steel Washer l3, nd provided with recesses which receive three equally-spaced pilot rollers l4 and three equally-spaced thread-forming rollers I 5, all of which rollers are mounted ing rollers are considered the most desirable,

zontal alignment.

but, depending upon the ductility of the material being worked upon and upon the character of the thread to be formed, a greater or less number of rollers may be used.

The pilot rollers I4 are mounted for rotation on the lower or forward ends of the drive pins in such a manner that, as the tool is rotated in a. tube or other hollow work piece, the circle circumscribed by the high or Work-contacting portions of these rollers is substantially normal to the inner surface of the work piece. This may be accomplished by providing a slight radius .on

the outer or contacting surface of each of these rollers. The drive pins are held in the body'members I and II by a drive fit, and the rollers II are held on the forward end of the drive pins by the steel washer I3.

As shown in Figs. 1 and 4 the drive pins I5 are each mounted in the body members I0 and II at a slight angle to the vertical and the thread-forming rollers I5are each mounted for rotation on a drive .pin with the longitudinal axis of the rollers coincident with the longitudinal axis of the drive pins. With this arrangement the rollers I5 are mounted in the body members with the transverse axis thereof inclined slightly from the transverse axis of the body members, which inclination may be termed the lead angle of the rollers. Also, as shown in Fig. 4, the three rollers I5 are not in 'hori Reading from left to right, the .secondof these rollers is slightly higher than the first and thethird is slightly higher than the second. With the rollers stepped in this manner,jthe rolling edges on one roller will track in grooves started by the preceding rollers.

As shown, particularly in Fig. 8, each of the rollers I5 is provided with four individual annular rolling edges or-teeth I'I, I8, I9 and 20, with the external diameter of the teeth increasing uniformly from tooth II to tooth I9, and with tooth of slightly .less external diameter than tooth I9. The spacing of teeth I! and I8 is the sameas that of I8 and I9. However, the space between teeth I9 and 20 is greater than that between II, III and I9. As shown, tooth 20 is much sharper than teeth I1, I3 and I9. With this arrangement the threads are formed gradually, with teeth I'I, I8 and I9 forming one continuous helical thread, and with tooth 20 forming a second continuous helical thread by splitting the ridge of the first formed helical thread into two-ridges, thereby forming two continuous helical threads.

It has been found in practice, for example, in forming very fine helical threads or capillary grooves on the interior wall of a tube, that by spacing the teeth Il, I8 and I9 approximately .050 inch apart and by spacing the tooth 20 a distance of .075 inch from tooth I9 excellent results are obtained. There is a definite relationship between the spacing of teeth I'I, I8 and I! and that of tooth 20. In the example given the space between teeth I9 and 2a is one and one half times that between teeth I'l, I8 and I9. If more than two continuous helical threads are to be formed, additional splitting teeth may be applied to each of the rollers and the spacing of the teeth may be computed in accordance with the character and number of threads desired.

If desired, each of the rollers I5 maybe provided with follow-up or bottoming teeth spaced rearwardly of the splitting teeth 20 .so .as .to smooth out or dress up the parallel threads formed by the splitting teeth. With the use of one splitting tooth, as shown, at least two followup teeth, not shown, would be used on each of the rollers I5. These additional teeth would be so located on each of the rollers that at least one such tooth will track in each of the helical grooves formed by the rolling and splitting teeth. Follow-up rolling teeth are well known in the art and since these teeth per se form no part of my invention, it is not necessary that they be shown or described in detail. It is suflicient to say that the number of such follow-up teeth required on each roller is dependent upon the number of parallel threads that are formed by the splitting teeth.

As shown in Fig. 7, the machine screw I2 is provided with a socket head 2I which receives a wrench or the like, not shown, for adjusting the screw. A driving head 22 provided with a drive shaft 23 fits over the free ends of the drive pins I6 for rotating the tool. The shaft 23 may be rotated by any suitable mechanism, such as an electric motor or the like, not shown.

In operation, a tube, or other hollow work piece, on which threads are to be formed is clamped in a suitable fixture, not shown, in such manner that thetube is held stationary, and in a manner that the tube cannot be expanded by the tap. With rotary motion applied to shaft 23 the tap is rotated as it is inserted in one end of the tube and the pilot rollers l4 align the tap in the tube and iron out any irregularities on the interior wall thereof. The diameter of the path circumscribed by the rollers I4 as the tap is rotated is but slightly less than the internal diameter of the tube. The diameter of the path circumscribed by the teeth or threadforming edges of the rollers I5 is slightly greater than the internal diameter of the tube. As the thread-forming rollers I5 reach the inner wall of the tube, the longitudinal axis of therollers being at a, slight angle (lead angle) to the longitudinal axis of the tube, the first tooth ll of each of these rollers unites in pressing or rolling a helical groove in the tube wall while at the same time building up a helical ridge thereon, then the second .tooth I8 of each of the rollers travels in the groove made by the first tooth deepening the groove and increasing the height of the ridge, then the third tooth I9 travels in the groove deepened by the second tooth, deepening this groove still further and building the ridge still higher, and finally the fourth tooth 20 of each of the rollers presses a helical groove in the ridge formed by the teeth I1, I8 and I9. In pressing the second helical groove in the tube surface, the tooth 20 forces the material built up into the ridge by teeth II, II! and I9 laterally in both directions thereby partially closing the relatively wide groove formed by the latter teeth. When the tap .reaches the other end of the tube, two continuous helical threads which are relatively deep and narrow will have-been formed on. the interior wall of the tube from one end of the tube to the other end thereof .with one pass of the tap through the tube. After reaching the other end of the tube, the tap is disconnected from its rotating mechanism (not shown) and the threaded tube is removed from its clamping fixture (not shown). As shown in Fig. 8, the groove A formed by teeth II, It and I9 is relatively wide and the grooves B formed by tooth '20 by partially closing groove Aare relatively narrow.

As stated at the outset of this specification, there 'is no material removed from the tube walls in forming the helical threads thereon. Rather, a helical groove is formed by a rolling or kneading action, with the first tooth ll of each of the rollers rolling a helical ridge on the wall of the tube, the second and third teeth l8 and I9 rolling or squeezing the material into a progressively higher ridge, and the fourth tooth 20 splitting the ridge formed by the other teeth thereby doubling the number of threads per unit length of tube. By properly spacing the rolling and splitting teeth and by using the correct lead angle, any multiple thread can be made with a single pass of the tap through the tube. It is to be noted that the taper and spacing of the teeth l7, l8 and I9 is such that these three teeth, which are quite sturdy, are depended upon for pulling the tap through the tube, and that the tooth 20 of each of the rollers is depended upon only for rolling the second helical groove into the helical ridge formed by the other teeth.

Since the tooth 20 of the rollers plays no part in pulling the tap through the tube, this tooth may be made much sharper than the teeth l7, l8 and I9, so that for forming two continuous helical threads only one such tooth is needed on each roller. By providing three threadforming rollers equally spaced around the circumference of the tap in stepped relation, and with the teeth or rolling edges of these rollers tapered and spaced, as pointed out above, the wear on the individual teeth is appreciably reduced. Should one or more of the thread-forming rollers become worn or damaged in use, such roller may be easily replaced by removing the drive pin upon which the roller is mounted.

In the particular structure disclosed, first a single helical thread and then a double helical thread is formed on the tube as the tap passes therethrough. However, as pointed out above, by properly spacing the teeth on the rollers and by using the correct lead angle, any multiple helical threads may be made with one pass of the tool through the tube. Furthermore, for purpose of illustration, the invention has been incorporated in a tap for forming a multiple of fine threads or capillary grooves on the interior Wall of a tube or other hollow work piece. The invention may, however, be incorporated with equal facility in a tool in the form of a die for forming fine threads or capillary grooves on the exterior wall of a work piece. I, therefore, wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

What is claimed is:

l. A tool for forming a multiple helical thread on a surface of a work piece comprising a body member, a thread-forming roll having ribs thereon rotatably mounted on said body member for gradually forming a helical groove in said surface while simultaneously forming a helical ridge thereon, and ribbed roll means cooperating with said threading roll and arranged relative to said threading roll so as to divide the helical thread formed by said threading roll into a plurality of helical threads.

2. A tool for forming multiple threads comprising a body member, a plurality of rollers mounted in spaced relation around a periphery of the body member, a plurality of individual rolling edges formed on each of said rollers in uniform spaced relation along a portion of the length thereof, the diameters of the rolling edges increasing from the front toward therear of each of the rollers, said rolling .edges being adapted to form a thread on the surface of a workpiece, and an additional rolling edge formed on the rearward portion of each of said rollers and spaced from the rearmost of said plurality of rolling edges a distance greater than the uniform space between the plurality of rolling edges, said additional rolling edges being so constructed and arranged as to divide the threadformed on the workpiece by the plurality of rolling edges to a plurality of threads.

3. A method of forming multiple threads on a surface of a workpiece which comprises forming grooves in said surface while simultaneously forming ridges between the grooves, squeezing material outwardly of the ridges to increase the height thereof and ,to thereby increase the depth of the grooves, and splitting the ridges intoadditional ridges with grooves therebetween thereby forming multiple threads on the workpiece surface.

4. A method of forming capillary grooves in a tube surface which comprises flowing material from the tube surface into a helical ridge while forming a helical groove in said surface between the helical ridge, deepening the helical groove by flowing material outwardly of the helical ridge, and subseqeuntly splitting the helical ridge into a plurality of helical ridges while simultaneously forming a plurality of helical grooves in the tube surface between the helical ridges.

HOMER E. PFINGSTON.

References Cited in the file of this patent UNITED STATES PATENTS 

